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In this photo provided by Tasnim News Agency, family members of a plane crash victims weep in the village of Bideh, at the area that the plane crashed, southern Iran, Sunday, Feb. 18, 2018. An Iranian commercial plane crashed Sunday in a foggy, mountainous region of southern Iran, and officials said they feared all people aboard were killed.

Iranian search and rescue teams on Monday reached the site of a plane crash that authorities say killed all 65 people on board, Iran's Press TV reported.

The Aseman Airlines ATR-72, a twin-engine turboprop used for short-distance regional flying, went down on Sunday in foggy weather, crashing into Mount Dena in a remote area of southern Iran. The airliner said all on board Flight EP3704 were killed, including six crew members.

The crash of the aircraft, brought back into service only months ago after being grounded for seven years, was yet another fatal aviation disaster for Iran, which for years was barred from buying necessary airplane parts due to Western sanctions over its contested nuclear program.

Press TV said search teams reached the crash site before dawn on Monday. The station said the weather had improved, though it was still windy. The semi-official Tasnim news agency cited the military as saying Russia had helped locate the crash site. Russia and Iran are close military allies.

The TV broadcast footage of a helicopter joining the search and showed ambulances and rescue vehicles preparing to reach the site on Mount Dena, which is about 4,400 meters (14,400 feet) tall. The site is reportedly at a height of 3,500 meters (11,500 feet).

Other Iranian news outlets and officials did not confirm that the crash site had been reached. State radio said five helicopters and five drones are active in the search operation. Iran's semi-official ISNA news agency said that more than 150 climbers have joined the operation.

Transport Minister Abbas Akhoundi left Tehran on Monday to visit the site of the crash, state TV reported. Footage posted on independent news websites showed him in the cockpit of a plane taking part in the search. State TV quoted him as saying the cause of the crash was still "not clear."

High winds have made it difficult to fly helicopters and drones, hampering search efforts.

The 2015 nuclear accord with world powers lifted international sanctions on Tehran in exchange for curbs on its nuclear enrichment program, allowing Iran to purchase airplanes and airplane parts. The country has since signed deals to purchase tens of billions of dollars' worth of new aircraft. However, President Donald Trump's refusal to recertify the deal has injected uncertainty into those sales.

The ATR-72 went down near its destination, the southern city of Yasuj, some 780 kilometers (485 miles) south of the capital, where it took off.

It wasn't immediately clear what caused the crash, although weather was severe. Dense fog, high winds and heavy snow in the Zagros Mountains made it impossible for rescue crews in helicopters to reach the site in the immediate aftermath, state TV reported.

Aseman Airlines spokesman Mohammad Taghi Tabatabai told state TV that all on board Flight EP3704 were killed. The plane had 59 passengers and six crew members, the state-run IRNA news agency reported late Sunday, lowering the initially reported death toll of 66.

The United States expressed condolences over the crash in a Farsi-language statement posted on social media Sunday.